摘要/Abstract
氢键对于蛋白质等生物分子的结构与功能具有重要影响.基于近红外光谱对含氢基团的高灵敏响应及其温度效应，研究了脂肪胺中氮氢基团的结构及相互作用.采用独立成分分析对不同温度、不同浓度样品的光谱进行分析，得到光谱中的三种独立成分，分别对应于氮氢基团的非氢键键合、线型氢键键合和环状氢键键合三种结构形式.随着温度的升高，两种键合形式的氮氢基团逐步转化为非氢键键合形式.环状键合的氮氢基团先解离为线型键合形式，再解离为非氢键键合形式.随着脂肪伯胺侧链的增长，NH基团的光谱吸收受温度影响减弱，且线型键合形式受温度的影响较环状键合形式小.
关键词: 近红外光谱, 温度效应, 脂肪伯胺, 独立成分分析, 氢键
Temperature dependent near-infrared (NIR) spectroscopy has been developed for structural analyses, especially for the study of hydrogen bonding, due to the distinct influence of temperature on both intra-and inter-molecular interactions. In this work, the hydrogen bonding of primary aliphatic amines (amylamine, hexylamine and heptylamine) were studied using the NIR spectra measured from 25 to 80℃ with a step of 5℃. Continuous wavelet transform (CWT) was applied to enhance the resolution of the NIR spectra, and independent component analysis (ICA) was adopted for analyzing the temperature effect. High resolution spectra were obtained by CWT, from which the peaks of free and hydrogen-bonded NH groups can be identified. The results obtained by ICA show that three independent components (ICs) can be obtained, corresponding to the spectral information of the free, linearly and cyclically hydrogen-bonded NH groups, respectively. Therefore, with the reconstructed spectra from the three ICs, the variation of the three forms of NH groups with temperature can be analyzed. When temperature increases, the hydrogen-bonded NH groups transform into the free form, and the cyclic form dissociates through the linear form. Furthermore, NIR spectra of the amines in carbon tetrachloride (CCl4) solution were measured at 25℃ in the concentration range of 0.1~1.0 mol/L. The three ICs can also be obtained by ICA from the spectra after CWT. From the variation of the ICs with concentration, it was shown that NH groups in the amines prefer to be linearly aggregated at low concentration, but the cyclic aggregation increases with the increase of concentration. In addition, a comparison was performed on the results obtained by ICA from the spectra of the three amines measured at different temperatures. The result shows that there is no obvious difference for the temperature effect of the three amines, the variation of the three forms of NH groups with temperature, however, is different. With the increase of the carbon chain length, the variation of free and cyclically hydrogen-bonded NH group slows down, but there is a slight increase for the change rate of linearly hydrogen-bonded NH group. Therefore, temperature dependent near-infrared (NIR) spectroscopy may provide a new tool for studying the hydrogen bonding in liquid and solution samples with the help of chemometric calculations. The method may be promising for analyzing the complicated interactions in bio-systems, particularly the hydrogen bonding or inter-and intra-molecular interactions.
Key words: near-infrared spectroscopy, temperature effect, primary aliphatic amine, independent component analysis, hydrogen bonding
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